The present invention relates to a sensor to determine total temperature, true airspeed and Mach number of an air vehicle moving through an air mass, and the static temperature of the air mass using two or more thermometers or temperature sensing elements with known, but different temperature recovery factors. One relatively unobtrusive instrument permits the determination of these parameters without large, outwardly projecting probes.
It is well known that temperature sensors or thermometers have different temperature recovery factors. The recovery factor of a thermometer is a standard measure that defines how well the thermometer “recovers” the total kinetic energy imparted to it so the thermometer will sense and indicate the true total air temperature in a moving air stream. The recovery factor is the difference ratio of the sensed temperature minus the static temperature to the total temperature minus the static temperature. If all kinetic energy could be recovered, i.e., if the air could be brought adiabatically to rest at the thermometer location, the recovery factor would be one. A high recovery factor is desired when designing total temperature sensors. It has been known that the geometry of the thermometer largely dictates its recovery factor, and the known difference in recovery factors between two or more thermometers or temperature sensing elements is utilized in the present invention for determining the desired temperature parameters, as well as true airspeed and Mach number.